If the closing
of the curtain halfway at the Presanctified Liturgy has nothing to do with
veiling the already-consecrated Lamb, while leaving the unconsecrated wine
unveiled, then what is the basis for this unique rubric?

The hypothesis that the curtain is used to
veil the consecrated Gifts during the Presanctified Liturgy contradicts the use
of the curtain at the full Divine Liturgy, where the curtain is closed fully
after the Great Entrance, when the Gifts are not yet consecrated, but is opened
for their consecration and remains open after their consecration until the
communion of the clergy.

Nikol'sky, in his "Aid to the Study of the
Liturgical Typicon of the Orthodox Church," writes as follows:

'At the Liturgy of the Presanctified Gifts,
after the transfer of the Holy Gifts, the curtain is partly closed (its first
half) and opened (its second half). It is closed for the same reason that it
remains closed also at the full Liturgy after the Great Entrance, namely that the
Entrance recalls the going of the Lord to His passion and is the unattainable
mystery of the salvation of men, hidden from many ages and generations (Col 1:26)
-- the mystery of the bloodless sacrifice of the Lord, "who is the God of
ineffable and invisible mysteries, and with whom are the hidden treasures of
wisdom and knowledge" (prayer at the Presanctified Liturgy after the Great
Entrance). The curtain ought to be open after the Great Entrance, during the
Litany before "Our Father," for the reason that at this time it remains open also
at the full Liturgy. As at the full Liturgy, so also at the Liturgy of the
Presanctified Gifts, at this time the consecrated Gifts are on the Holy Table,
and the people (with the curtain open), while contemplating the sacrifice offered
for the sins of the world, call with boldness upon the Heavenly God as Father and
say: "Our Father."'

According to Nikol'sky, then, the
half-open, half-closed curtain after the Great Entrance at the Presanctified
Liturgy serves two functions:

the function of the closed curtain after
the Great Entrance at the full Liturgy and

the function of the open curtain during
and after the consecration of the Holy Gifts at the full Liturgy.

Following this line of thinking, it would
be reasonable for the curtain to be closed from south to north, precisely so that
the open side, i.e., the left side, would correspond to the same side of the Holy
Table (the left side) on which the discos with the consecrated Lamb has been
placed. That way the consecrated Lamb would be open to the contemplation of the
people before the Lord's Prayer, just as it is at the full Divine Liturgy. This
reasoning, then, is the exact opposite of the idea that the curtain is intended
to veil the consecrated Gifts from view.

In general, I think that the history, use
and significance of the curtain is something that needs a lot more study and
elucidation.